1. Field of the invention
This invention relates to intraocular lenses (IOL's) and more particularly to intraocular lenses wherein the optic member of the lens is axially displaced from the supporting points within the eye.
2. Brief description of the prior art
The implantation of an intraocular lens (IOL) to restore vision after the extraction of a cataractous crystalline lens has come to be a common procedure. Such lenses have been implanted in the anterior chamber or posterior chamber of the eye, and a variety of methods have been developed for fixing the lenses in their proper position. The typical intraocular lens comprises a central lens body (often called the "optic") which replaces the original crystalline lens of the eye, and supporting structures (often called "haptics") which are fixed to the optic and extend therefrom so as to support the lens centrally within the eye. The haptics generally comprise structural elements extending radially from the optic so that when in place within the eye they engage the surrounding ocular tissues and provide support for the lens portion. It is common to use haptics which are flexible strands or filaments of biologically inert material which extend radially from the central lens and support it by pressing against the surrounding tissue.
When intraocular lenses are implanted in the anterior chamber of the eye, the haptics commonly contact the anterior chamber angle. When implanted in the posterior chamber, the haptics may be placed either in the residual portion of the lens capsule, if present, or in the ciliary sulcus, immediately behind the iris. In either position of implantation, care must be taken to prevent the lens from contacting the iris and blocking the pupil, for such a blockage will prevent the flow of aqueous humor through the pupil and result in an elevated intraocular pressure. It is also important to prevent the lens from rubbing against the iris. Such rubbing can result in dispersion of the pigment in the iris, which is referred to as pigmentary dispersion syndrome. This syndrome can lead to the formation of translucent sections of the iris, and in turn a condition known as pigmentary glaucoma. Finally, it is additionally important to prevent contact between the lens and the iris in order to avoid the possibility that the lens will be captured by the pupil upon contraction or dilation of the iris, which may result in displacement of the lens, as well as other problems.
In response to the above-cited concerns, the intraocular lens designs of the prior art have included configurations wherein the haptics or supporting loops extend anteriorly from the optical portion of the lens. Such configurations are generally referred to as "vaulted" posterior chamber lenses. When such a "vaulted" lens is implanted, the outer ends of the haptics may be located adjacent to the peripheral iris in the ciliary sulcus, capsular bag or anterior chamber angle, while the lens body is axially displaced away from the pupillary opening of the iris.
Two general styles of vaulted lenses especially adapted for posterior chamber implantation have been developed. In the so-called "step-vaulted" design, the segment of the haptic nearest the optic extends in an angled direction out of the plane of the optic, usually at a relatively large angle, e.g., about 20.degree., while the distal segment is constructed parallel to the plane of the lens. In this design the outer segment of the haptic runs generally parallel to the plane of the iris, and consequently this segment of the haptic may come into contact with the iris creating a serious potential for injury.
In another type of vaulted IOL the haptic extends from the periphery of the optic at a constant angle to the plane of the optic along its length until it reaches the designed radial distance. This design, commonly referred to as an "angled" form of vaulting, avoids the problem of excessive contact with the iris, but introduces a drawback in the procedure for implantation. It is customary to implant the IOL in the eye after the removal of the cataract by sliding it laterally at a slight angle through the small incision below the cornea, through the iris and into the posterior chamber. It is also customary to fill the cavity caused by the removal of the cataract with a viscoelastic material, e.g., hyaluronic acid, in order to maintain the shape of the cavity from which the crystalline lens was removed and protect the delicate tissues of the eye. However, as the IOL is being moved laterally into the viscoelastic-filled posterior chamber, the angled haptic tends to be deflected by the drag of the viscoelastic material as it is moved therethrough, because the haptic, particularly the leading edge is presented to the viscoelastic face at a relatively high angle of incidence.
Accordingly, a need has continued to exist for a vaulted intraocular lens that avoid both the problem of contact with the iris and that of excessive deflection of the haptic during implantation.